Stem cells may cause tumours: US study

Injecting human embryonic stem cells into the brains of
Parkinson's disease patients may cause tumours to form, U.S.
researchers reported on Sunday.

Steven Goldman and colleagues at the University of Rochester
Medical Center in New York said human stem cells injected into rat
brains turned into cells that looked like early tumours.

Writing in the journal Nature Medicine, the researchers said the
transplants clearly helped the rats, but some of the cells started
growing in a way that could eventually lead to a tumour.

Various types of cell transplants are being tried to treat
Parkinson's disease, caused when dopamine-releasing cells die in
the brain.

This key neurotransmitter, or message-carrying chemical, is
involved in movement and Parkinson's patients suffer muscle
dysfunction that can often lead to paralysis. Drugs can slow the
process for a while but there is no cure.

The idea behind brain cell transplants is to replace the dead
cells. Stem cells are considered particularly promising as they can
be directed to form the precise desired tissue and do not trigger
an immune response.

Goldman's team used human embryonic stem cells. Taken from
days-old embryos, these cells can form any kind of cell in the
body. This batch had been cultured in substances aimed at making
them become brain cells.

Goldman's team apparently succeeded and transplanted them into
the rats with an equivalent of Parkinson's damage. The animals did
get better.

But the grafted cells started to show areas that no longer
consisted of dopamine-releasing neurons, but of dividing cells that
had the potential to give rise to tumours.

The researchers killed the animals before they could know for
sure, and said any experiments in humans would have to be done very
cautiously.

Scientists have long feared that human embryonic stem cells
could turn into tumours, because of their pliability.

Opponents of embryonic stem cell research cite such threats.
Many opponents, including President George W. Bush and some members
of Congress, believe it is immoral to destroy human embryos to
obtain their stem cells.